Characteristics of a galactose-binding hemagglutinin (lectin) from hemolymph of Spodoptera exigua larvae

Abstract

Hemolymph from Spodoptera exigua larvae agglutinates rabbit and human O erythrocytes. The agglutinin appears to be naturally occurring i.e., injury (by injection) or injection of larvae with fungal cells does not induce an increase in titer of hemolymph samples. Hemagglutinin activity is destroyed by heat or EDTA, and galactosidic carbohydrates inhibit agglutination of both red blood cell types. The agglutinin was purified by affinity chromatography using an Affi-Gel ovalbumin column. Binding to the column is calcium (cation) dependent. SDS gel electrophoresis shows that the agglutinin is a minor component of whole hemolymph represented by two bands with molecular weights of 30,500 and 31,000 daltons. Fluorescence microscopy using rhodamine-labeled agglutinin indicates that the agglutinin binds to fungal cell wall surfaces known to have galactose residues (e.g., Paecilomyces ochraceus), and that binding is specifically inhibited by galactose. There is no specific binding to fungal walls known to lack galactose residues (e.g., Paecilomyces ochraceus, Nomuraea rileyi). The agglutinin may be involved in the immune response of the insect e.g., by opsonization of microbial (fungal) surfaces which render the invading cells more susceptible to phagocytosis or agglutination.